Apparatus and method for detection of radiation

ABSTRACT

Digital images or the charge from pixels in light sensitive semiconductor based imagers may be used to detect gamma rays and energetic particles emitted by radioactive materials. Methods may be used to identify pixel-scale artifacts introduced into digital images and video images by high energy gamma rays. Statistical tests and other comparisons on the artifacts in the images or pixels may be used to prevent false-positive detection of gamma rays. The sensitivity of the system may be used to detect radiological material at distances in excess of 50 meters. Advanced processing techniques allow for gradient searches to more accurately determine the source&#39;s location, while other acts may be used to identify the specific isotope. Coordination of different imagers and network alerts permit the system to separate non-radioactive objects from radioactive objects.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application claims priority from U.S. Provisional Application No.60/656,980 entitled, “APPARATUS AND METHOD FOR DETECTION OF RADIATION”filed Feb. 28, 2005, U.S. application Ser. No. 11/364,027 entitled,“APPARATUS AND METHOD FOR DETECTION OF RADIATION” filed Feb. 28, 2006,now U.S. Pat. No. 7,391,028, issued Jun. 24, 2008 and U.S. applicationSer. No. 12/123,879 entitled, “APPARATUS AND METHOD FOR DETECTION OFRADIATION” filed May 20, 2008, all of which are hereby incorporated byreference in their entireties.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable

PARTIES TO A JOINT RESEARCH AGREEMENT

The United States Government may have certain rights to this inventionpursuant to work funded thereby at the TRANSIT RESEARCH BOARD (TRB) OFTHE NATIONAL ACADEMY OF SCIENCES under grants from IDEA Grant No.TRANSIT-42.

BACKGROUND

1. Field of Invention

Not applicable

2. Description of Related Art

The ability to detect the unauthorized transportation of radioactivematerials would be facilitated by a large-scale network of radiationsensors. However, the installation of such a network of radiationsensors would be costly and delay the readiness of the system.

Radiation sensing networks are being developed in Europe in case of anuclear power-plant accident. For example, the Real-time On-lineDecision Support (RODOS) system for off-site emergency management inEurope is being planned to provide consistent and comprehensiveinformation on present and future radiological situations, the extent,benefits and drawbacks of emergency actions and countermeasures, andmethodological support for making decisions on emergency responsestrategies. RODOS includes geographical, meteorological and radiationpropagation detection modules; it also serves as a data accumulationpoint for radiological and atmospheric monitoring networks. Radiationsensing data provided by networked detectors would complement and enrichthe radiation database like RODOS available to security authorities anddisaster recovery agencies.

The ability to detect the unauthorized transportation of radioactivematerials over a wide area is pressing due to the break-up of countrieshaving nuclear weapons and nuclear reactors. Radioisotope smuggling andblack market sales of radioactive material has increased substantiallyin the recent past. A General Accounting Office report documents some ofthe International Atomic Energy Agency's (IAEA) 181 confirmed cases ofillegal sales of nuclear material since 1992. Twenty of these incidentsinvolved the transfer or attempted transfer of nuclear weapons useablematerial, namely Pu-239 and 20%-90% Highly Enriched Uranium (HEU).Although the most ominous risk from rogue radiological material isrelated to HEU's use in the construction of a nuclear bomb, HEU couldalso be used as the raw material for a Radiological Dispersal Device or“dirty bomb”. Indeed, any radioisotope can be used in the constructionof a dirty bomb. However, some radioisotopes, for example Cs-137, Sr-90,or Co-60 are more dangerous than others for this application. Forexample, U-235, due to its comparatively low level of gamma rayactivity, is not nearly as dangerous as a comparable mass of Co-60.Dirty bombs would be economically devastating to a region due to thehigh expense for decontamination, clean up, and economic loss should onebe detonated.

Radioactive material dispersed via the detonation of a conventionalexplosive would be economically devastating to the region affected.Access to non-weapons-usable nuclear material is typically easier thanto HEU or Pu-239, magnifying the dirty bomb threat arising fromnon-weapons-usable materials. This threat is heightened by the fact thatnuclear contraband is typically smuggled in quantities that rarelyexceed one kilogram and that nearly all of the smuggling cases weredetected due to police investigations. The clean-up costs from even thissmall amount of radioactive material could be tremendous. It is betterto detect the illegal transport of radiological materials and interdictit at an early stage.

A need exists for detecting the illegal transportation of radioactivematerial. There is a need for a cost effective and wide spread networkof sensors that can detect radioactive material, identify its location,and provide an alert when this type of material is detected.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention include a system that includes animager with one or more pixels that are capable of interacting with highenergy particles and relaying information with reference to theinteraction of the high energy particle with the pixel whilesimultaneously obtaining an image. The system may also include at leastone processor that is in communication with the imager, which is able todetermine that a pixel or pixels have interacted with one or more highenergy particle. The system may further include an output device thatreports the presence of the high energy particle.

The imagers may be any imager containing a pixilated photon detectorincluding charge coupled device (CCD) imagers, complementary metal oxidesemiconductor (CMOS) imagers, and imagers containing silicon-germanium,germanium, silicon-on-sapphire, indium-gallium-arsenide,cadmium-mercury-telluride or gallium-arsenide substrates and the like,or combinations of these imagers. Security cameras, traffic cameras,transit cameras, hand held cameras, mobile law enforcement or trafficcameras, cell phone cameras, thermal infrared cameras, and anycombination of these cameras may also be used in embodiments of thepresent invention. The imagers used in the current invention may bestationary or movable. In a preferred embodiment of the invention, theimagers are able to rotate about a vertical axis, or pan, and rotateabout a horizontal axis, or tilt. This allows the imager to track theposition of the source of radioactive source of the high energyparticles.

In certain embodiments, high energy particles detected by the imager orimagers may be the product of a source of high energy particles whichmay be the source of nuclear decay of radioactive material. The sourceof high energy particles include, but are not limited to, ambientradiation, radiation from natural sources, radioactive materials,nuclear devices, dirty bombs and nuclear weapons either before or afterdetonation or combinations thereof. The high energy particles detectedmay preferably be produced from the nuclear decay of radioactivematerials. The source of high energy particles may also be shielded.

The pixels of pixilated photon detector produce a signal when a highenergy particle strikes the pixel, and this signal is generally strongerthan that of ambient, background radiation. This signal may be a brightspot or “dot” on the image created by the imager. The processoridentifies these dots. When a high energy particle strikes a pixel thecharge of the pixel changes more significantly than when ambient lightstrikes the pixel causing a dot to form since the imager reads thischange in charge as a bright spot on the image. The processor of thepresent invention identifies dots within the image and compares them tobackground. If the processor detects the dot in consecutive images, aradiation event may have occurred.

In one embodiment of the present invention, the processor is able toidentify the presence of a radioactive particle as well as the source ofthe radioactive particle. The processor may be a computer, a video imageprocessor, a human or any combination of these.

In another embodiment of the present invention, the imager contains athin square of pixels. The likelihood of a high energy particle strikingthe thin square of pixels is at a maximum (maximum flux) when the thinsquare of pixels is perpendicular to the source of the high energyparticles. The likelihood of a high energy particle striking the thinsquare of pixels decreases as the imager is panned and/or tilted awayfrom the source or the source moves through the imagers field of view.In certain embodiments, the processor is able to perform a gradientsearch to determine the maximum flux by driving the movement of one ormore imagers until maximum flux is reached. In yet other embodiment,several imagers perform a gradient search concurrently. The processorcan then reference each imager and compare the photographic and or videoimages obtained from the imagers to determine the likely source of thehigh energy particles as the area where the images intersect. Theimagers are preferably interconnected.

The movement of a source of high energy particles may also be determinedover time thereby allowing the movement of the source to be followed. Ina preferred embodiment of the current invention one or more imagersperform gradient searches while concurrently obtaining images of thearea surrounding a radioactive source. The images and maximum flux arecompared to the images and an object or objects in the images may beselected as likely containing or holding the radioactive source. Theobjects can be any animate or inanimate objects including for example,motor vehicles, airplanes, trains, subway cars, people, animals,buildings, vegetation, luggage, boxes, bags, handbags, briefcases, mail,and combinations thereof.

The images obtained by the imagers may contain or illustrate themovement of objects within the view of the camera. In one embodiment ofthe present invention, objects are mixed between images and/or imagersallowing the source of the high energy particles to be located. In apreferred embodiment, a visual determination of the source of highenergy particles is made.

Output devices useful in embodiments of the present invention include analarm system, a photographic or video image, an image on a monitor, anaudible sound, a telephone call, a radio transmission or multiples orcombinations of these.

In further embodiments of the present invention, the type of radioactivematerial or radioisotope that is producing the high energy particles canbe determined. The number and energy of the high energy particles may bequantified based in the change in charge of the pixel with which thehigh energy particle has interacted. This quantification may be comparedto a library of charge changes based on the type of radioactive materialproducing high energy particles and used to determine the amount and/ortype of radioactive material in the source.

In certain embodiments, detection may be checked for false positivedetection of radioactive material either prior to or followingactivation of an alarm system. These and other features, aspects, andadvantages of the present invention will become better understood withregard to the following description, appended claims, and accompanyingdrawings.

DESCRIPTION OF DRAWINGS

FIG. 1 depicts the pixel coordinates of gamma-ray strikes on the CCD ofa test bed digital video camera. The data are summed over 15 seconds ofvideo and represent almost two gamma-ray hits per second with only 16 μCof radioactivity, located 1.5 cm from the CCD detector.

FIG. 2A shows an astronomical image from a CCD detector before analysisand identification of high energy particles in the image; FIG. 2Billustrates the identification of signals due to high energy particlesinteracting with the pixels.

FIG. 3 illustrates the signal that would be expected to be measured fora moving source of radiation as measured using versions of the apparatusand methods disclosed.

FIG. 4 illustrates how two separate detectors, for example networked CCDtraffic cameras, can be used to separate radiation producing or highenergy particle emitting objects from other objects which are notproducing or carrying harmful radioactive material.

FIG. 5(A-D) depicts control experiments performed using a Logitechwebcam, a CCD based device, collecting 15 seconds of video at 15frames/s. FIG. 5(A) refers to “Control-1”, FIG. 5(B) refers to“Control-2”, FIG. 5(C) refers to “Control-3” and FIG. 5(D) refers to“Control-4”.

FIG. 6 (A-C) illustrates results from experiments performed with 16 μC'sof radioactive source material, as described in Table 1 and Table 2.

FIG. 7 illustrates a flow diagram for the acquisition and analysis ofimages from a pixilated detector capable of detecting high energyparticles emitted from nuclear decay of radioactive materials accordingto an embodiment.

FIG. 8 illustrates the acquisition and analysis of images from one ormore imagers capable of detecting high energy particles emitted fromnuclear decay of radioactive materials according to an embodiment.

FIG. 9 depicts a flow diagram for the acquisition and analysis of imagesfrom one or more imagers capable of detecting high energy particlesemitted from nuclear decay of radioactive materials according to anembodiment.

FIG. 10 depicts a flow diagram illustrating a routine for acquiring andprocessing images from a pixilated imager to locate evidence of gammarays emitted by a material according to an embodiment.

FIG. 11 depicts a flow diagram illustrating a routine for acquiring andanalyzing images from a pixilated imager to locate evidence of gammarays emitted by a material according to an embodiment.

FIG. 12 depicts a flow diagram illustrating a routine for analyzingimages from a pixilated imager to locate evidence of gamma rays emittedby a material according to an embodiment.

FIG. 13 depicts a flow diagram illustrating a routine for providing awarning or alarm to a user or command center and providing tracking ofthe source and or further analysis for determining the location,movement, or type of radiation emitting source material according to anembodiment.

FIG. 14 illustrates a non-limiting example of an apparatus for detectinggamma rays emitted from a material utilizing a pixilated detector.

FIG. 15 schematically illustrates one or more fixed or mobile detectors,each capable of movement or translation detecting high energy photonsfrom a radioactive material according to an embodiment.

FIG. 16(A) illustrates the images from a detector without gamma raydetections, and FIG. 16(B) with gamma ray detections as white flecks(inside white circles).

DETAILED DESCRIPTION

Before the present compositions and methods are described, it is to beunderstood that this invention is not limited to the particularcompositions, methodologies or protocols described, as these may vary.It is also to be understood that the terminology used in the descriptionis for the purpose of describing the particular versions or embodimentsonly, and is not intended to limit the scope of the present compositionsand methods which will be limited only by the appended claims.

It must also be noted that as used herein and in the appended claims,the singular forms “a”, “an”, and “the” include plural reference unlessthe context clearly dictates otherwise. Thus, for example, reference toa “gamma ray” is a reference to one or more gamma rays and equivalentsthereof known to those skilled in the art, and so forth. Unless definedotherwise, all technical and scientific terms used herein have the samemeanings as commonly understood by one of ordinary skill in the art.Although any methods and materials similar or equivalent to thosedescribed herein can be used in the practice or testing of embodimentsof the present invention, the preferred methods, devices, and materialsare now described. All publications mentioned herein are incorporated byreference. Nothing herein is to be construed as an admission that theinvention is not entitled to antedate such disclosure by virtue of priorinvention.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Pixilated image detectors, such as charge-coupled (CCD) devices andcomplementary metal oxide semiconductor (CMOS) devices, may utilize alight-sensitive pixilated chip containing semiconductor material tocreate modern digital still and video images. While these pixilatedchips have been effectively used to create conventional CCD and CMOScameras, such chips may also be sensitive to high-energy particles andmay be used as detectors for astrophysical sources of X-rays and gammarays, digital X-ray mammography, and for high-energy physics experimentsat particle accelerators.

Pixilated chips may be used in a variety of image detectors includingbut not limited to still or video cameras, camera phones, webcams,netcams, security cameras, traffic cameras or any combination of these.These image detectors may be easy to use, readily available, directlydigitize data, interface with computers easily, have exceptional quantumefficiency, low noise and a linear response to photon energy, highenergy particles and gamma rays emitted from sources of radioactivematerial. When a photon, gamma ray, or high energy particle strikes apixel in the light-sensitive pixilated chip, electrons may move into theconduction band of the material providing a charge or potentialproportional to the number and energy of particles incident andtransparent to the pixel. Thus, higher energy photons may produce largernumbers of counts within the affected pixels allowing the processor todetermine light versus shadow and the color of the light. However in thecase of a high energy particle or gamma ray, static-like bright spotsusually 1, 2 or 4 pixels in size may be created on the resulting imageallowing for the identification of high energy particles and potentiallyradioactive material. Furthermore, the brightness of the spots maydepend upon the energy of the particle that strikes the pixel. As such,the type of radioactive material may also be determined using devicescontaining light-sensitive pixilated chips.

A “pixel” refers to a detector element unit cell for convertingelectromagnetic radiation to signal electrons by the photoelectriceffect. The generated charge may be collected and may depend upon thenumber of pixels and/or the amount of charge the pixels can hold. Theformation of a particular well for a pixel may depend upon the dopantand concentration and that different processing techniques may be usedto tailor the doping profiles to optimize a sensing operation for aparticular energy of electromagnetic radiation. Substrates for pixelsmay be a p-type silicon substrate, however other options may also beused, such as, p on p⁻ substrates, or p on p⁺ substrates, SOI, BiCMOS orthe like. Further, other semiconductor substrates, for example,silicon-germanium, germanium, silicon-on-sapphire, and/orgallium-arsenide substrates, among many others may be used. It should beunderstood that pixels may be aligned in an M×N array accessed using rowand column select circuitry.

Detecting radioactive material may involve sorting through environmentalmonitoring data for the effects of high energy particles, neutrons, orgamma rays (γ's) emitted from the spontaneous decay of fissionableisotopes. Nuclear decay may generally involve the ejection of an alphaparticle (Helium nucleus) or beta particle (electron or positron) withenergy in excess of one MeV (Million Electron Volts=1.6×10⁻⁶ ergs).Gamma ray photons may also be emitted from the nucleus duringspontaneous decay, with energy in the range of about 10 KeV to severalMeV, depending on the isotope and decay mode. The measurement of eachphoton's energy may be performed using a variety of detectortechnologies.

The method for detecting the presence of signals characteristic ofphotons striking the pixilated detector is composed of steps. When it isdetermined that a statistically significant increase in signal in animage or pixel has occurred as the result of high energy particlesstriking the detector (e.g. 25% above normal background), for asufficiently long amount of time (e.g. for 3 or 4 images in a row), a“radiation event” may be taking place. A radiation event may refer to anincrease in the ambient level of radiation that is deemed to be inexcess of normal statistical fluctuations.

If the counts or identity of an event measured by a detector isdetermined to be hazardous, an alert may be initiated by communicatingrelevant information to a network-aware layer. Optionally, advancedcommand, control, coordination activities may be initiated, including agradient search to localize the source within the camera's field ofview, perform triangulation from multiple cameras, and stream alert andvideo to designated individuals/computers. For cameras with a fixedknown position, the position of the camera may be used to approximatethe location of a source or radioactive material. In addition, theposition of one or more fixed cameras may be included in calculations totriangulate the location of the radioactive material.

In one embodiment, in the case of two-dimensional radiation location, acomputer or processor may use the information received from one or morecameras including camera location and image data to compute radiationintensity, identify a type of material identity, compute an approximateposition, or any combination of these. The location of the radiation fora small source identified may be approximated from initial images andfurther refined or tracked with subsequent images from the cameras. Theextent of a plume of radiation may be monitored based on images andcounts from the cameras. Any of several different optimizationprocedures may be used to optimize the position of an identifiedradiation source. In one embodiment, the processor may first obtain arough estimate of the object's location by a conventional method such astriangulation. Other optimization approaches may also be used. Forexample, a standard technique, such as an iterative progression throughtrial and error to converge to the maximum, may be used. Also, agradient search may be used to optimize the position of a source. Themethod may be extended to three dimensions to select a point x, y, z asthe best estimate of the radioactive object's location in threedimensions.

Pixilated image detectors that can produce charge carriers in responseto interaction with a photon or energetic particle may be used toprovide radioactive detectors. Pixilated image detector-equipped camerashave become ubiquitous for security, transit and traffic monitoring.Non-limiting examples of such image detectors may include CCD and CMOScameras including pre-existing security or monitoring cameras thatutilized these imaging processors. These detection devices may typicallybe networked and monitored from an operations center and, when combinedwith firmware or software, may be used to determine whether one or morepixels have a charge or voltage corresponding to a high energy particleor gamma ray interaction and to detect ambient radiation and radioactivematerials, the amount and type of material that is emitting high energyparticles and the movement of a radioactive material that is the sourceof the detected high energy particles.

For example, when the detector is near (e.g., less than 100 meters forenergy of about 3 MeV or less) a radioactive source a correspondingincrease in the rate of gamma rays striking the pixilated image detectormay result. Because the level of background radiation is low (e.g., <10counts/second per square inch), the presence of small quantities ofradioactive material may be found using pixilated imagers. The charge ofa pixel in an imager may be inferred from the brightness of the pixel inthe image. Alternatively, the charge or voltage from the pixel duringthe readout process may be used directly. The imager may then relatethis information to a processor that interprets the information andsounds an alarm.

In addition to sending the images and position of the CCD or CMOSimager, the imager unit may also be configured to transmit encodedinformation, such as the orientation of the camera, the temperature ofthe location, the time and the like.

In a monitoring configuration, the system or apparatus may performcontinuous sampling. The system or apparatus may acquire a digital imageof the environment or an object from a digital camera or digitaldetector. In a fast survey configuration, the system may be configuredto perform non-continuous sampling from one or more images taken ondemand or at longer intervals than that described elsewhere.

The sensitivity of the imager to different high energy photons may bedetermined using count information and calibration data from bothmodeling and empirical experiments. For example, an imager may beexposed to a series or known radioactive materials, such as Co-60,U-235, Bi-214 and the like, at a known distance. The charge orbrightness, frequency of counts, and ratio of intensities (charge orbrightness) may be determined. This information may be used to calculatethe energies of gamma rays detected by the imager.

Simulations using the “MCNP” software package developed by theDiagnostics Applications Group of Los Alamos National Lab (Los AlamosNational Laboratory Report, LA-10363-MS (1995)) may be used to show thatthe detectors and system described can provide statistically significantdetections of a wide range of radioactive species. Experimental resultsconfirming the utility of this model are illustrated in successfullydetected Cobalt-60 and Cesium-137 using 1-10 μC samples as shown in FIG.1.

Gamma rays may be emitted by radioisotopes at specific energies that arecharacteristic of the emitting nucleus' internal structure. A gamma raydetector able to determine the energy of individual photons may,therefore, unambiguously identify the type of nucleus that emitted theradiation. This type of spectroscopy is similar to optical spectroscopyin that the detection and identification of just a few features issufficient to characterize the source of radiation. Whereas opticalspectroscopy may often be photon starved and require the collection ofnumerous photons at each discrete wavelength, gamma rays have so muchenergy individually, that each gamma ray photon that interacts with apixilated image detector may lead to a statistically significant datafeature. The unique energy spectrum of gamma rays emitted from aradioactive material may be used to differentiate false detection fromreal detection.

An energy spectrum for gamma rays striking pixels in an imager may beobtained from an analysis of the image. Radioisotope identification viagamma-ray spectroscopy may involve reference library look-ups,comparisons, and decomposing a gamma spectrum into spectra fromindividual isotopes. The type of comparison may include thecross-correlation technique, which is a technique often used forcomparing spectra having multiple lines; a variety of matchingalgorithms for spectral and time-series applications; PrincipalComponent Analysis; combinations of these; or combinations that includeany of these. Therefore, analysis software may be developed thatmeasures this brightness of the spot, determines the energy spectrum ofthe particle and compares this information to a library spectra to allowthe identification of the particular radioisotopes emitting high energyparticles. The software may be used to distinguish gamma rays emitted,for example, by Co-60, as compared to Cs-137. Subsequent images may beanalyzed as needed to confirm the results of the identification, or thecounts or identity of the material obtained from one imager may becompared to other nearby detectors to confirm the results of the firstdetector. If the energy spectrum from multiple detected gamma raysmatches a harmful material a warning may be issued.

More specifically, an estimate of the statistical significance of eachindividual gamma ray photon may be obtained by comparing its interactionwith the detector with the effect that a single optical photon has onthe detector. The number of electrons counted per photon may depend onboth the energy of the incident photon and the instrument's gain,typically expressed as electrons per ADU (analog/digital unit). Ablue-light photon having 4 eV of energy will produce, on average, 3.1photo-electrons in a particular pixel for a Kodak KAF-1001E CCD (aparticular model CCD used in high-end digital image applications). Aninitial estimate may be that a 200 KeV gamma ray would yield 3.1e-/ADU*200,000 eV/4 eV=165,000 photo-electrons. However, only a portionof the gamma ray's energy may be transferred to the pixilated chip. TheMCNP model simulations may suggest that the transfer of energy issignificant. For example, a 766 KeV photon produced in a U-238 decaywill produce ˜500 photoelectrons (“counts”) while a 1.001 MeV γray willproduce ˜2000 counts. These numbers may be a lower limit of counts fordetecting a gamma ray as they include energy deposition in the siliconpart of the upper area of the pixilated chip. It is likely that themetal leads, SiO₂ covering, doping impurities or other factors maymodify or enhance the transfer of energy into the pixilated chip. Thesecounts may permit firmware or software to be used to identify the one ormore pixel locations at which the high energy gamma ray was depositedbased on the number of counts over a threshold. The total counts or thenumber of photoelectrons produced by a gamma ray, or a valueproportional to this, may be based on the charge or voltage produced bythe one or more pixels in the detector due to the gamma ray.

When analyzing materials which potentially emit detectable energeticparticles from one or more radioactive sources, the system and methodsmay be used to analyze or estimate the level of radioactive sources inthe material based on the amount of signal received from the CCD or CMOSdetectors. Variations in the amount and type of radioactive sources,shielding, the amounts and types of material in which the emitters arepresent or dispersed in, the geometric distribution of emitters in asample, versions of the system and detectors may be used to characterizethese features of the source.

Simulations using the “MCNP” software package for the expected countrate arising from various shielded radioisotopes were performed and itwas determined that a CCD detector may be used to monitor a largevariety of radioactive materials. Contributions to source shielding arepossible, and the simulations included: 1 mm lead shielding,self-attenuation within the radioactive source, two sheets of ⅛″ thicksteel, to represent a vehicle or a container's body panels, and a sheetof plate glass (conservative estimate of detector window) and a variabledistance air-gap. The gamma ray intensity may depend upon material, typeand amount, distance, geometry and shielding. Even when the absolutenumber of gamma rays detected is low, the individual gamma rays mayachieve very high significance because of their high energy and thespectral signature of those gamma rays unique to the isotope.

It is reasonable to expect that the lower limit of precision fordetermining the energy of a gamma ray that interacts with the imagerwould be the Signal-to-Noise Ratio (SNR) of the counts for individualdetections. This precision may be approximately equal to the square-rootof the counts associated with individual gamma ray hits on thelight-sensitive chip. The energy precision may be written as theuncertainty in energy (ΔE) divided by the Energy (E), or ΔE/E. Forstrictly Poisson statistics,

ΔE/E≈(#counts)^(1/2)/(#counts)=1/(#counts)^(1/2)

Noise may typically result from three sources: read-out electronics,dark current, and statistical uncertainty of the source countsthemselves (shot-noise). Read-out noise may be predominantly determinedby the quality of the electronics. Modern pixilated image detectors andcontrollers typically have a very low level of noise.

Dark current may be a CCD or CMOS imager chip specific value, usuallyexpressed as the number of electrons per pixel per second, on average,which accumulate during an “exposure” or image integration period. Darkcurrent counts may accumulate regardless of whether light or gamma raysthat are transparent to the electrodes are hitting the chip. The totalof such counts may depend upon the rate and total integration time. Therate of accumulation may depend strongly on the CCD or CMOS temperature,where the rate may roughly double for each increase of 6-10° C. of thechip. The effect of dark current upon image quality, and therefore theability to detect gamma rays with as little computational effort aspossible, may be insignificant for short integration times with moderncameras in good repair. By basing the detector, for example, on a videosystem with a frame-rate of roughly 10 to 20 frames per second, the darkcurrent, even when the chip is warm, may be negligible compared to theexpected hundreds to thousands of counts per gamma ray. This largesignal may ensure excellent counting statistics and aid in energydetermination, enabling accurate identification of radioactive sourcedespite ambient radiation in the local environment. While changes intemperature may be used to modify or detect ambient noise for a CCD orCMOS imager, unlike Ge based sensors, the CCD or CMOS detectors do notneed to be cooled to detect high energy particles.

Shot-noise may generate the most significant source of noise forsecurity cameras. Model calculations suggest that a 1 MeV photon wouldbe expected to have an uncertainty in the energy determination ofapproximately 1/(2000)^(1/2)=0.022, or 2.2%. Laboratory measurementsshow the measured counts for a lower-energy gamma ray photon fromCesium-137 to be about 200 counts, with an implied uncertainty of ˜7%per spectroscopic feature. Since most radioisotopes that emit gamma rayshave multiple energies, the unique spectral fingerprint may bepreserved, even with these error estimates.

Variation in the number of gamma rays that strike the detector may beeliminated using statistical methods, and the use of more than onedetector may also be used to account for these variations.

FIG. 2B illustrates that astronomical software or other similar softwaremay be used to isolate, analyze and/or quantify detector signals whicharise in digital image data from high-energy particles striking thelight-sensitive chip. The small circled dots may result from high energygamma rays striking the detector while the large bright spots may bestars that were the actual target for this image. It would be reasonableto expect that a source of radioactive material emitting high energyparticles would produce images with spots similar to the small circleddots and may be used to detect, identify, and/or quantify the source ofa known or unknown radioactive material.

Using one or more pixel based detectors capable of detecting andcharacterizing energetic particles, a moving radioactive source emittingdetectable energetic particles may be observed. The light-sensitive chipwithin the pixilated image detector may generally be in the form of athin square. When the thin square is positioned perpendicularly to thesource of the light or high energy particles, the probability of thephoton or high energy particle striking a pixel within the chip may bemaximized. This phenomenon is referred to as maximum flux. Theprobability of a photon or high energy particle striking a pixel withinthe chip may decrease as the source moves through the field of view ofthe detector. Therefore, as the source of high energy particles movesthrough the field of view of a static pixilated image detector (See FIG.3), the number of high energy particles striking the light-sensitivechip may increase over time as the source maintains a perpendicularposition (time=0) in regard to the chip and may decrease until thesource has left the detector's field of view (time=±20).

A pixilated image detector that is capable of moving may also beutilized to identify the source of photons or high energy particles.Movement of a detector, such as but not limited to, being panned,rotating along a vertical axis, and tilting, rotating along a horizontalaxis, may be able to perform a gradient search, whereby the camera isrotated horizontally or vertically until maximum flux is determined. Inthis way, one or more pixilated image detectors may identify thelocation or track the movement of the photons or high energy particlessource.

Buses, ferries, trains, patrol cars, or other transport vehicles areoften outfitted with security cameras, which may be used to detectradioactivity. Such cameras may also serve as roving detectors. In anembodiment, the metal sides of the cameras may not be significantlythicker than that of cars.

Although the use of a single detector may provide important informationabout a radioactive material, even more information may be obtained whenadditional detectors are used together and their outputs are combined.Computer programs may be used to integrate the output from severaldetectors. One advantage of the disclosed system and methods may benetworking detectors or cameras in close proximity to one another.Another advantage of the disclosed system and methods may be the abilityto network existing detectors or cameras in close proximity to oneanother. Many different topologies of networks of monitoring stationsmay be used. For example, in one version, multiple monitoring stationsmay be established by using the existing security cameras. If aradioactive source were to be carried past these detectors, separate“radiation events” may be detected at each imager or camera. Trains,buses, passenger cars, people and/or animals with radiation emittingmaterial moving near an imager may be expected to show a radiationprofile. Similar scenarios may apply for people on a train platform,buses on the road, or vehicular traffic at a bridge/tunnel. Wheremultiple detectors are in proximity to one another, it may be reasonableto expect each to have a time-series response similar in shape to thatshown in FIG. 3, but having different intensities or lack of symmetry,depending on the motion, speed, and position of the source with respectto the imager.

By networking the detectors, the speed and direction of the vehicle orindividual carrying a material that emits high energy particles likegamma rays from a radioactive source may be determined. Although incrowded road or urban settings it may not be possible initially touniquely identify a vehicle or person, a carrier, in possession ortransporting a radioactive material, normal traffic shear and mixing mayseparate the carrier of radioactive material from the other vehicles andpedestrians that are initially considered potential carriers.

In general, there may be more than one object of interest (person, car,package, suitcase, etc.) in the field of view of the detector. However,when the radioactive source has traveled or been carried to the nextcamera, it is likely that some of the original surrounding objects(people, cars, packages, suitcases, etc) will no longer be in closeproximity to the radioactive source, as illustrated in FIGS. 14(A) andFIG. 14(B). Therefore, as radiation events are picked up by sequentialcameras, the identity of the specific object containing or carrying theradioactive source may become better constrained. Sequential detectionsby a series of cameras may help to eliminate the innocent bystanders orvehicles from those being identified as the source of the radioactivematerial. These sequential detections may also serve to significantlyreduce or eliminate false-positive detections.

FIG. 4A and FIG. 4B illustrates the state of the traffic at twoarbitrary time periods (A) and (B). A truck 412 may emit high energyparticles 422 that are detected by CCD or CMOS detector 416A; detector420A is illustrated not detecting high energy particles emitted by thetruck source 412. The detection of high energy particles 422 by detector416A may trigger an alert that can be used to signal detector 420A to bemoved by a controller in the direction of the truck. Detector 416A maybe panned in the direction of the source of the high energy particles422 emitted by truck 412 to track the source of the high energyparticles. In FIG. 4B, detectors 416B and 420B have both been movedrelative to their positions in FIG. 4A. Detector 416B detects highenergy particles 426 and detector 420B detects high energy particles 428emitted by moving source 412.

In a transit environment, the importance of networked cameras is likelyto yield even faster, more robust identification of a source of materialor an object responsible for emitting high energy photons that can bedetected. For example, typical metro stations and similar facilities aredesigned to have at least two security cameras able to view the entirestation. Simultaneous detections by these CCD or CMOS cameras may beused to provide an important corroboration on detected radiation,increase confidence in warnings or alerts issued, and aid in makingtactical decisions. Moreover, since there are radiation absorbing,concrete walls in many stations, security cameras may detect the sudden“appearance” of a radioactive source. In such a situation, it may bepossible to uniquely identify the individual or source responsible forthe detector signal.

The pixilated image detectors used for high energy photon energydetection may contribute to a node in a network of radiation monitoringsites. Such cameras can sample their local radiation environment. Anyincrease in radioactivity may be identified, verified, and communicatedto the relevant emergency response center or centers. The identity ofthe radioisotope(s) by the system and cameras may also be communicated.If a large-scale release of radioactivity occurred, whatever the cause,functioning nodes may communicate the ambient activity level, permittingthe rapid mapping and forecasting of the spread of radioactive debris.The large-scale monitoring of radioactivity and alert capability may bemore wide-spread as transit or other security systems are installed,such as the Federal Highway Administration's implementation of anintelligent highway system.

The pixilated image detection system may further include alertpropagation and command and control protocols. Data collected by one ormore detectors may be gathered and transmitted to appropriatedestinations for action or storage. Multi-jurisdictional concepts ofoperations for situations that cut across facility, local, state, and/orfederal areas of responsibility may be facilitated in this manner.Common Internet protocols may be used to enable users to view videoframes and updated alert data in real-time on standard PCs and wirelessmobile handheld devices. These systems may be deployed ubiquitously withsupport for legacy infrastructure to ensure a reliable, secure andscalable platform.

Referring to FIG. 9, a method for detecting gamma radiation isdescribed. In step 908, a CCD or CMOS imager may collect an image of anarea, volume, or combination of objects. In step 912, any high energyparticles, such as gamma rays from the decay of a radioactive material,in the area imaged may strike the imager or one or more pixels in theimager creating an artifact in the image. In step 916, the image fromthe imager may be analyzed for artifacts from high energy particles. Forexample, the charge may be determined for individual pixels of theimage, and/or the image may be analyzed to determine the brightness ofthe pixels. The image may be analyzed for objects imaged by the imagerand artifacts due to gamma rays. In step 932, a determination may bemade as to whether artifacts in the image from gamma rays interactingwith the detector are present. If no artifacts are produced from gammaray interaction, the routine may continue to step 944 and adetermination may be made as to whether to continue image collection. Ifartifacts are produced from gamma ray interaction, the routine maycontinue with step 920 where additional images or frames of the area maybe taken. In step 924, a determination may be made as to whether theartifacts persist in the image. If the artifacts do not persist, theroutine may return to step 908. If artifacts persist, a warning thatgamma rays were detected may be issued. In step 928, intensivemonitoring may be initiated. This may include a gradient search ofimages that have artifacts, evaluation of images from other cameras,scanning or panning cameras, issuing additional alerts, and/or otheracts to identify the source.

FIG. 10 refers to an embodiment of a method for processing images takenby a still or video imager. In step 1008, the image from a camera may beconverted to a file format for further processing and input into memoryin step 1012. The image pixels may be evaluated using one or more testsand comparisons to find artifacts in the image from gamma rays in step1016. A determination may be made in step 1020 as to whether the pixelpassed all the tests that would indicate that a gamma ray was detected.If such tests are not passed, the next pixel may be evaluated. If suchtests are passed, the location of the pixel may be marked or indicatedand the pixel count may be increased in step 1028. The next pixel maythen be evaluated. A determination as to whether all the pixels in theimage have been evaluated may be performed in step 1032. If additionalpixels remain to be evaluated, such pixels may be evaluated. Otherwise,a determination may be made in step 1036 as to whether any gamma rayswere detected in the images. If gamma rays were detected, a warning maybe issued in step 1040. Otherwise, the routine may terminate or the nextimage may be evaluated.

FIG. 11 is an embodiment of a method for the detection of gamma raysusing a CCD or CMOS imager. In step 1104, a user may request an image orcontinuous imaging of an area or objects by the imager may occur. Theimager may collect data in step 1108 and analyze 1112 the image forbrightness or pixel charge. A determination may be made as to whetherhigh energy photons or gamma rays were detected in the image. If not, adetermination may be made as to whether to continue acquiring images orto stop the image collection. This determination in 1124 may becontinued until a user input is made to stop collecting data. If highenergy photons or gamma rays are detected, further image analysis may beperformed in step 1120. Once the image analysis is complete and theresults returned, a determination as to whether to continue the imagecollection may be made in step 1124.

Referring to FIG. 12, an embodiment of a method for analysis of an imageis illustrated. The method may include flagging the image as one where agamma ray detection event was detected in step 1204. Next, adetermination in step 1208 as to whether a sufficient number of imageshave been flagged for detected radiation may be made. If so, an alarm oralert may be issued. If not, the imager may be instructed in step 1220to collect an additional image. The image may be analyzed for artifactsdue to gamma rays that have interacted with the imager. In step 1232, adetermination may be made as to whether gamma rays were detected in theimage. If gamma rays are detected, the image may be flagged as adetection event in step 1204 and the routine may continue. If not, adetermination may then be made in step 1224 as to whether to continueimage collection. If so, the routine may return to step 1204.

An example of a method for generating an alarm or alert is illustratedin FIG. 13. Where an alarm is requested, the routine may provide awarning indication in step 1308. A determination as to whether toperform additional image analysis or scans may be made in step 1312. Ifadditional analysis is requested, additional images may be obtained, agradient search of the image, or analysis of multiple images to identifythe source, or analysis and comparison of images from multipledetectors, or scanning a detector(s), other analysis, or a combinationof these may be performed in step 1316. A determination may be madebased on the analysis and results from step 1316 as to whether tocontinue the analysis. If so, step 1316 may be repeated and additionalimages and or analysis may be obtained. If not, the routine mayterminate.

FIG. 14 illustrates a non-limiting example of an apparatus for detectinggamma rays emitted from a material utilizing a pixilated detector. Theapparatus may include a controller 1420 that may receive information orimages from a detector 1408, may implement instructions, and mayoptionally be used to control the movement or the position of thedetector 1408. A receiver 1404 may be used to input instructions to thecontroller. The receiver may include, but is not limited to, a keyboard,cable, radio waves, or a computer. A transmitter 1424 may be used tosend data, images, or instructions to another remotely located stationusing cables, phone lines, radio waves, or other methods ofcommunication.

The system illustrated in FIG. 14 may include a central processing unit(CPU) 1420 having corresponding input/output ports, read-only memory(ROM) or any suitable electronic storage medium containingprocessor-executable instructions and calibration values, random-accessmemory (RAM), and a data bus of any suitable configuration. Thecontroller may receive signals from a variety of individual pixels orfrom the pixilated imager or detector sensors coupled to cameras orstand alone detectors, and/or as part of a vehicle. The processing unit1420 may be used to control the operation and/or motion of the sensors,a view taken by the sensors, and/or accept and output information to orfrom the sensors detectors. The controller may be connected to an inputdevice 1404, such as a keyboard. The controller may perform dataanalysis or send information from detectors to a central processing unit1404. Information from the sensors may be provided directly to areceiving station or through a transmitter 1424 in a known manner.

FIG. 15 schematically illustrates one or more fixed 1524, movable 1504and 1556, or mobile 1552 detectors, each having a CCD or CMOS detector1508, and each capable of detecting high energy photons from aradioactive material source 1520, which may be encased in a shieldingcontainer 1516. Each of detectors 1504, 1524, 1552, and 1556 maycommunicate the images to a receiver by cables or telephone lines 1536,1540, 1564 or by radio waves 1548. The receiver 1544 may be interfaced1568 with a computer or other control and analysis system 1560.

Camera phone and other portable devices, for example 1552 in FIG. 15,may be configured for remote placement and interconnection with anetwork of other sensors. These devices may be solar powered and may bedesigned to connect to the network in the event that one or moreenergetic particles are detected. Portions of a network of detectors maybe activated to detect energetic particles when one or more primarydetectors senses energetic particles having energies within one or morepredetermined energy windows or above a threshold amount. The activatednetwork may monitor the movement of the radioactive source material.

Some radioisotopes are easier to detect than others. The calculationsand examples in the disclosure are based on U-235, which compared toCo-60 is more difficult to detect, and serve as a guide to theapplicability of radiation detection systems based on semiconductormaterials where the counts produced by a photon incident on a pixel isproportional to the energy of the incident gamma ray produced by thesource of radiation. Although the examples and calculations disclosedherein are based on U-235, the system, methods, and apparatus may beused for the detection of high energy photons from any radioactivematerial that undergoes nuclear decay. These CCD and CMOS imager deviceshave a linear response to the incident photon energy. While U-235 may beused as an example of a material that produces detectable high energyphotons, the claims and disclosure are not limited to any particularradioactive material.

Instructions or programs, which may be in firmware (computer programscontained permanently in a hardware device (as a read-only memory)),EPROM, or software, may include various routines that identifyradioisotopes according to the energy spectrum of the detectedradioactivity. These programs may also include the capability to acceptand analyze data from remote networked digital cameras, issuedistributed alerts, and use network infrastructure to coordinatedetections from multiple detectors. Versions of the system for detectingand identifying radioactive material with pixilated imagers may be usedto form an inexpensive, dense network of radiation detectors. Such adetector network may supply continuous real-time detection and trackingof radioactive sources over a wide area and range of environments, suchas highways, factories, cities, hospitals, other institutions, and otherurban or rural locations.

For example, FIG. 2A shows a portion of a typical astronomical CCDimage. The spots that result from high-energy particles, cosmic rays,ambient radioactive sources, and gamma rays striking the CCD during theexposure may be identified using an automatic identification program.This system may perform real time identification once the detectionparameters are set. Due to the uniformity of CCD light detectioncharacteristics, setting the detection parameters may only be performedonce for a given type of camera. Once a prototype camera is set up,other systems using that specific type of detector may operate using thesame settings or with only a short calibration check.

Instructions and routines in software or firmware may be used todetermine the statistical significance of each peak pixel outputcompared to the ambient noise. The routines may begin with a scanthrough the image data, looking for very high count-rate pixels. Theroutines may further include comparing high count-rate pixel peaks toneighboring pixels using statistical tests. The statistical tests mayinclude minimum thresholds, minimum ratios (peak to neighbor), use ofdetector and electronics characteristics, or combinations of testsincluding these. Statistical tests and programs may be used to providedetection probabilities with low false-positive outcomes. Additionalchecks and comparisons of the detector signal may be used to furthersuppress spurious alerts.

Potential sources of false-positive outcomes include backgroundradiation, Cosmic Rays (CRs), sudden increases due to rain washing fromthe air naturally occurring decay products of Radon-222, Bismuth-214 andLead-214, and the decay of Ra-222 itself. Background activity mayusually be very low, as is the system noise, so detection of bona fideradioactive sources may be accomplished with a very high degree ofstatistical confidence. Data screening tests of information receivedfrom detectors and cameras may be used to minimize false-positiveoutcomes. These may include tests for appropriateness of detectedspectra and persistence of the signal in multiple exposures. Inaddition, a vehicle or person carrying nuclear material may trigger oneradiation event after another. Such a moving detection may clearlyidentify a bona fide source, and may not arise from backgroundradiation, cosmic rays, or any other local radiation artifact. Finally,a large radiation release may yield distributed, persistent activityover the region affected.

In conclusion, a system and method for the detection and identificationof radioactive isotopes may include an apparatus based on asemiconductor material that may obtain photographic or video images ofobjects and simultaneously detect high energy particles that interactwith digital still and video camera imagers. The apparatus may use CCDand CMOS based images. These detector or imagers and other digitaldetectors of electro-magnetic radiation and charged particles, may, inaddition to detecting light, detect energetic particles and high-energyphotons emitted from radioactive isotopes. The images from the one ormore CCD or CMOS imagers may be transferred to a computer using a framegrabber or imaging board connected by, for example, a cable or a PCI busto a processor. Images may also be transferred using infrared datatransfer, radio waves, or other electromagnetic waves used incommunication devices. The images may be stored on a disk for retrievaland further analysis; the images may be stored in a compressed format.Image sequences may be captured at full or reduced frame rates. Imagedata from the imagers may be sent to acquisition equipment and then tothe data processing equipment, including computers and other digital oranalog data manipulation and analysis machinery. An analysis of imagedata transferred from the above components of the system may be used todetect the presence of radioactivity.

An analysis of the images from one imager may be compared to analyzedimages from other nearby imagers to determine if a false-positiveconclusion has occurred. Nearby cameras should be able to detect gammarays detected by the first imager and the energies and ratio of energiesdetected should be similar and may be compared using statistical andlogic-based tests to verify the persistence and/or consistency of theradioactivity measured. The location of hot spots or bright spots in animage due to gamma rays emitted from a terrestrial source of radioactivematerial may be used with the images of objects in the imager's field ofview to locate the position of the radioactivity.

Various aspects of embodiments disclosed will be illustrated withreference to the following non-limiting examples. The examples below aremerely representative of the work that contributes to the teaching ofthe present invention, and the present invention is not to be restrictedby the examples that follow.

Example 1

This example illustrates the ability of an imager to detect high energyparticles and illustrates the sensitivity of the detector.

The functionality and sensitivity of the various imagers to detect gammarays (still and video) from different manufacturers were performed. Ineach experiment, the cameras were operated, without modifications,according to their standard directions. Exposures were alternately madewith and without radioactive material near the camera body. The imagestaken without a nearby source served as control experiments. In general,it was expected that very few of the control experiment images shoulddisplay the small pixel-scale dots caused by radiation strikes on thedetector. It is also reasonable to expect some, but not necessarily all,of the images (also called frames, exposures or collectively data) tocontain such artifacts.

In one series of laboratory tests, a digital video camera manufacturedby Logitech, specifically, the Quickcam for Notebook Pro was used. Thatcamera contains a 1280×960 pixel Charge-Coupled Device (CCD). In asecond series of tests, an Olympus Camedia C-700 digital still camera,which contains a 1600×1200 CCD was used. Both cameras were exposed,without modifications, to small, unregulated radioactive sources. Whenexposed to these sources, gamma rays were successfully detected as verysmall, distinct white dots.

When collecting radiation sensitivity data, three radioactive sources(see Table 1): (1) 1 μC Cobalt-60, (2) 5 μC Cesium-137 and (3) 10 μCCesium-137 were used. These sources were ordered from SpectrumTechniques, Inc. of Oak Ridge, Tenn. Spectrum Techniques providescalibrated radiation sources for experimental laboratory work. TheCobalt-60 source emits powerful 1.17 MeV and 1.33 MeV gamma rays. Theseenergetic rays are very penetrating, with only half of such gamma raysbeing absorbed after traversing 11 mm of lead. Cesium-137 emits 0.66 MeVgamma rays, which are about half as penetrating as are those from Co-60.Half of Cesium-137's gamma rays penetrate 5.5 mm of lead. The fact thatgamma-rays pass through significant amounts of lead shielding makes itvery unlikely that radioactive sources large enough to be dangerouscould be surrounded by enough shielding to avoid detection, if thesystem sensitivity is large enough. Preliminary results of sensitivityare discussed vide infra.

TABLE 1 Calibrated Activity Lead shielding Level per Spectrum NominalGamma-ray Beta decay required to Count rate Source Techniques Decaysenergy energy block half of from Quantex Number Radioisotope data sheetper second (keV) (keV) the γ-rays Geiger Counter 1 Cobalt-60 1 μC 37,0001173.2 317.9  11 mm 700 μR 1332.5 2 Cesium-137 5 μC 185,000 32 511.6 5.5mm 661.6 1173.2 3 Cesium-137 10 μC  370,000 32 511.6 5.5 mm 661.6 1173.2

In order to assess the ultimate sensitivity of the method, Geiger-Mullercounter data were collected under as nearly identical conditions aspossible to the Logitech webcam CCD data. The detector chosen was aQuartex model RD8901, manufactured by Quarta in Russia. The detector'scalibration has been verified to be correct to within 10% accuracy atBrookhaven National Laboratory. The detector was positionedapproximately 1.5 cm from the sources, with a 1/16th inch thick piece ofacrylic plastic in between the source and detector. The plastic was usedto provide nominally equivalent shielding to that of the webcam cover.Normal operation for the Quartex detector is to collect data for 31 to33 seconds and then indicate the hourly radiation exposure level inmicro-Roentgen/hour. The resulting count rate average over a 6-minutesampling period is shown in Table 1 for the Cobalt-60 sample. The othersources overloaded the detector, and no reliable count rates wereobtained.

Results for system sensitivity. The Olympus camera was used just withsource #1. With the 1 μC Cobalt disk lying flat against the rear side ofthe camera, flush against its LCD view panel, there was one (1)gamma-ray hit in one of ten 0.5 second exposures. In 44 controlexperiments, with no radioactive source, there was no evidence of agamma-ray detection of the camera.

More extensive experiments with the Logitech webcam were performed thanwith the digital still camera. In each of the webcam experiments, datawere collected for 15 seconds, at 15 frames per second, to producemovies comprised of approximately 225 frames. Control experiments wereperformed first with the camera surrounded by lead bricks and coveredwith a thick black cloth. The second series of tests were identical,except that the Cobalt-60 and the two Cesium-137 sources were placednext to the webcam. The third series of tests had the camera uncovered,aimed at the ceiling of the laboratory, with no radioactive disk nearby;the lead brick over the camera was removed, but the side bricks werestill in place. The final series of tests used the same set-up as theprevious series, but for the inclusion of the two Cesium-137 sources.Details concerning the first two series of tests are discussed below andsummarized in Table 2.

The control experiments consisted of four 15-second video clipsrepresenting 996 individual data frames, each 66.7 ms in duration. Atotal of four energetic particle strikes on the CCD were detected (seeFIG. 5 (A-D) for pixel locations). These were presumably due tocosmic-ray impacts, or nearby radioactive decay of a naturally occurringelement such as Radon or its decay products, or some other ambientsource of background radiation. None of the four counts occurred closerthan a few seconds to the others. This temporal gap between counts, andor a minimum count-rate, can be used as criteria to trigger an alert andalso as part of a false-alarm suppression strategy.

FIG. 6 (A-C) show three sequences of images taken while the webcam satatop the three radioactive sources. The sequences were each 15 secondslong. This configuration detected 126 energetic particle strikes on theCCD among the 773 individual frames. The count rate varied between 1.6counts/sec and 3.5 counts/sec.

An estimate of the statistical significance of these detections can bemade to understand the value of the system as a warning device forradiation or for detection of ambient radioactivity. Consider separatelythe three “source” experiments having 24 counts (FIG. 6A), 49 counts(FIG. 6B) and 53 counts (FIG. 6C). The effective background radiationlevel was measured to be approximately one (1) count per 15 seconds ofdata in FIG. 5. Since radioactive decays follow Poisson distributions,and the number of counts per data set is greater than 20, some estimatesof the significance of the detections using Gaussian statisticsarguments may be made. The approximate 1-σ uncertainty in themeasurements is the square-root of the measurement, or: 4.9, 7, and 7.3counts, respectively for Source-1, Source-2, and Source-3. These valuesyield results of 24±4.9 counts/15-sec, 49±7 counts/15-sec, and 53±7.3counts/15-sec. The first value is a few standard deviations away fromthe other two values, it is possible that the webcam may have slidslightly toward the sources after the first experiment; if so, atranslation of ˜7 mm would account for the variation observed. Thesignificance of the detections, expressed in multiples of theirrespective 1-σ uncertainties, is:

significance=(value−background)/uncertainty

The resulting significance of the detection of the radioactive sourcefor the “Source-1” experiment is (24−1)/4.9=4.7σ. The correspondingvalues for “Source-2” and “Source-3” are 6.9σ and 7.1σ, respectively. Inthese experiments, it was known that there really was a radioactivesource nearby, but that will not always be the case. It would be usefulto know the likelihood for both false-negative and false-positiveresults. To determine the false-negative

${{Probability}\mspace{14mu} {of}\mspace{14mu} {false}\text{-}{negative}} = {\frac{1}{\sigma \sqrt{2\pi}}\exp \left\lfloor {\frac{- 1}{2}\left( \frac{{{background}\mspace{14mu} {value}} - {{mean}\mspace{14mu} {value}}}{\sigma} \right)^{2}} \right\rfloor}$

results, the probability that instead of recovering the expected numberof counts, a number close to the background rate is found. For countrates equal to those recorded in Table 2, the probability that astatistical anomaly would produce a false-negative can be calculated byevaluating the Gaussian Probability Distribution. This can be done for avalue equivalent to what would be considered normal for background, ascompared to the “Total number of gamma rays detected” (called “meanvalue” in equation below), using the 1-σ values. This probability is:

For Source-1, this probability is about 1 in 100,000, for Source-2 andSource-3 it is more than an order of magnitude lower. The system'ssensitivity therefore makes it very robust against false-negativeresults, i.e., if the ambient radiation is at least as intense as thevery low laboratory conditions, the count rate will be high enough tomake a detection. Moreover, a radioactive source will most likely benear a detector for an extended time, or else pass by multipledetectors. Therefore, the risk of missing a source is correspondinglyreduced by the number of 15 second periods spent near a detector.

To calculate the false-positive probability, the same equation would beused, except the background rate and mean value definitions arereversed, and the 1-σ now corresponds to that of the background countrate, which is correspondingly lower. For the extremely low backgroundrate observed, approximately 1 count per 15-seconds, the variance is illdefined from a Gaussian statistics perspective; a much longer exposurewould be needed to fix it firmly. However, a rough order of magnitudeestimate for the 1-σ, uncertainty would be ±1 count (the square-root of1). Using a value of 1 for σ means that a false-positive alert at thelevel of Source-1 would be a 25-σ occurrence, i.e. a formal probability<10⁻¹¹⁶. Additional analysis of the false-positive alert rate may bemade with more extensive determination of the background rate and itsvariance. The low background rate also helps to ensure that real alertsare handled appropriately, not lost in measurement noise.

TABLE 2 Laboratory Results Total number Number of frames in ExperimentTotal source # of individual of gamma-rays which gamma-rays Averagecounts Series activity (μC) video frames detected were detected persecond Control-1 0 224 0 0 0.0 Control-2 0 224 3 3 0.2 Control-3 0 225 00 0.0 Control-4 0 224 1 1 <0.1 Source-1 16 225 24 20 1.6 Source-2 16 22349 36 3.3 Source-3 16 225 53 41 3.5

Expected field sensitivity for imagers may be based upon scalingarguments using results of laboratory detections. The Federation ofAmerican Scientists performed a number of calculations to assess thelikely impact of various dirty bomb scenarios. The results of theirdetailed investigations can be found on the FAS website (FAS PublicInterest Report 55, N.2, 2002). One of these case studies considered thecase of a 10,000 Curie source of Cobalt-60. Such a source is 10⁹ timesmore active than the 10 μCi Cesium source and 10¹⁰ times more activethan the 1 μCi Cobalt source. In a preliminary calculation the sourcegeometry or self-shielding were not changed. As distance between sourceand detector increases, the main effect is a fall-off of intensity thatis proportional to the square of the distance between source anddetector. The laboratory detections took place with a 1.5 cm distance.With the above assumptions, for a source 10¹⁰ times more active than ourCobalt-60 source, a comparable detection could be made when it is(10¹⁰)^(1/2)×10.5 cm=1500 meters away, while a source 10⁹ times moreactive would be detectable roughly 470 meters away. However,air-attenuation becomes important for distances greater than roughly 100meters, at which point air becomes an important component of theshielding calculations. Since the calculated distances exceed thedistance over which air-attenuation becomes important, a conservativeestimate for an effective range for the detectors under these conditionswould be several hundred meters, however greater ranges are possible.Alternatively, at closer separations, a stronger signal of radioactivitywould be detected, or a less active source could be detected.

Example 2

This prophetic example illustrates the use of a CCD or CMOS camera orvideo camera to detect gamma-rays from a radioactive material.

One or more CCD or CMOS imagers may be used to sample a region orobjects in the environment to determine if radioactive materials arepresent. An image from each of the cameras may have the charge at eachpixel determined using the imager's hardware to detect pixels with highcharge caused by photoelectrons generate by gamma rays. Alternatively,the image may be analyzed using software or firmware from the camera ora central processor connected to the camera to detect gamma-rayartifacts. The data signature of a gamma ray may include one or morepixels having high charge or brightness above a background or thresholdlevel. The charge, brightness and frequency of the pixels struck by thegamma rays emitted from a source or radioactive material is expected tobe greater than the charge or brightness for the same pixels interactingwith ambient light or background radiation.

Software may be used to evaluate the images from an imager and conduct aseries of steps to reduce/eliminate false-positive alerts. These stepsmay include acquiring additional images; calibrating the detector;comparison of the image and detected high energy particles with imagesfrom other nearby cameras; comparing the counts to a threshold;comparison of the identity of the energy of the gamma rays detected witha library of known radioactive isotopes to determine if a match ispossible; assembling one or more images to determine if the radioactivesource is moving and if the detected high energy particles correspond tothe movement of the object in the image, or any combination of theseacts.

Where high energy particles above a predetermined level are detected inpixels or images from the imagers, warnings or alerts may optionally beissued to system operators or others if there is a persistent,statistically significant radiation artifact or signature in one or morepixels or images that correspond to a radioactive material.

Where high energy particles above a predetermined level and/or frequencyare detected, an intensive study of the images or pixels from thecameras can be performed to more precisely locate the source orradioactive material and identify its composition. Optionally, camerasdetecting gamma rays may be coordinated to triangulate the radiationsource location to a small volume and to improve specificity ofradioisotope identification. The location and identity of the detectedradioactive source may be disseminated to system operators or others inupdated alerts.

Example 3

One non-limiting way of checking the pixels or image from an imager isto evaluate the four closest pixels (4CP) in digital image data. If thepixel or image data point under consideration is (X,Y), then the 4CPare: (X+1,Y), (X,Y+1), (X−1,Y), and (X,Y−1). The local background valueof the imager can be taken as the average of the eight pixelscorresponding to (X−2,Y−2), (X,Y−2), (X+2,Y−2), (X−2,Y), (X+2,Y),(X−2,Y+2), (X,Y+2), (X+2,Y+2); alternatively if a known reference objectis in the field, it may be set to be the background and the average ofthe pixels or data points corresponding to the object set to thebackground.

In one mode of operation as illustrated in FIG. 7, a digitalcamera/digital video camera takes a picture (704) and in another stepthe digital image(s) may be transmitted to computer (708). The imagesmay be searched for specific signatures of gamma-ray strikes and mayalso include false positive tests (712). If evidence of a radioactivematerial is found, the test may be repeated with the next availableimage (718), otherwise begin again with the next image (718). Ifevidence still indicates bona fide detection of radioactivity, alerts orwarnings may be issued, intensive monitoring may be initiated, and datamay be transmitted to a second stage monitor for inter-cameracoordination 722.

Additional false positive tests, for example image-to-image “hot pixel”comparison (726), in which it is determined if the same pixel(s) is(are) detecting high count rates image after image. “Hot pixels,” iffound to be a problem, may usually be calibrated by one of severalcommon techniques.

Intensive monitoring may include performing a gradient search toidentify source (730), identify specific radioisotope(s) (734), and/orissue a warning (742). Analysis of multiple alerts enables the systemand operators to track and to identify the source of radioactivity(738).

The functions of the software or firmware for interpreting the imagesfrom a digital camera or pixel data from an imager chip having one ormore pixels are shown in FIG. 8. Data from the imager is collected 804.Digital cameras are sensitive to decay products of radioactive materials(energetic particles and gamma-rays). If radiological materials arenearby, some of the decay products may penetrate the camera body andstrike the digital detector, creating artifacts in the image 808.

Images from a digital camera may be analyzed for the presence ofartifacts 812. If no evidence of radioactivity is detected, imagecollection may continue 804. If evidence of radioactivity is detected,optionally repeat the analysis on one or more additional frames 816. Therepeated analyses may serve as a false-positive screen 816. The analysisof frames may be continued until a sufficient number of frames show aradioactive material is present (evidence persists) 820, or there is noradioactive material present (evidence for radioactive material does notpersist); for example the counts, image brightness, or charge on pixelsof the imager are consistently below a threshold 820). Where theevidence does not persist, image collection may continue 804.

If the evidence for the presence of radiation persists, an alert orwarning may be issued by the system 824. The detectors may performintensive monitoring by a gradient search to identify a detected source,not necessarily initially within image/video frame 828. Optionally,multiple alerts may be analyzed to track and identify the source ofradioactivity. As data are gathered, further alerts may be disseminated832. This information may include alerts collected from other digitalcameras 806.

In FIG. 8, digital images are collected from one or more cameras/videocameras 804. The cameras may be used for security purposes and may benetworked to an operation center. These digital cameras may be used towork as radiation detectors whether or not they are utilized for videosecurity monitoring. The detectors (e.g. CCD, CMOS, etc.) are sensitiveto energetic particles from radioactive decays. Gamma rays in particularare the most likely to both reach the detector and interact with it insuch a way as to be detectable. The detectors manifest this sensitivityregardless of the direction from which the gamma rays enter the camera.The physical size (e.g. in square inches) of the detector, and itsangular orientation, may determine the solid angle subtended by thedetector, from a radioactive source's perspective. A larger solid anglemay produce a higher rate of gamma rays interacting with the detector. Aradioactive source having a higher degree of activity (e.g. more decaysper second) may produce a higher rate of gamma rays interacting with thedetector. The data from each camera may be transmitted to a computerwhere the analysis is performed. The transmission may be via a cable,network, or electromagnetic radiation such as, but not limited to, radiowaves. At later stages of the detection and analysis process, theresults from two or more cameras may be combined to provide greaterdetail.

Digital cameras are sensitive to decay products of radioactive materialsenergetic particles and gamma-rays 808. If radiological materials areproximate, some of the decay products will penetrate the camera body andstrike the digital detector, creating artifacts in the image. In imagescollected from the detector, the absence of gamma rays may produceimages without white flecks FIG. 16 A; images or data with gamma raydetections may have white flecks FIG. 16 B.

The analysis procedure 812 may be run at specified intervals (e.g., 3times per second), on demand (e.g., click for analysis), as fast as thecamera can supply images and/or the computer or computers can analyzethem, or other modes. Decisions made at steps 824, 828, and 832 mayinfluence the mode for image selection and rate.

Each image may be converted to a file format suitable for furtherprocessing (e.g. FITS, SDF etc.). Suitable programs to transfer a fileinto a suitable format are known in the art and include GraphicConverter by Thorsten Lemke or other similar programs. An image may beread into memory. A search may be performed on this image to look forthe white flecks produced when gamma rays hit and interact with thedigital detector. A combination of algorithms may be used to detectgamma ray hits in an image. The intensity of the white flecks may beused to determine the energy of the gamma ray hits, and energy ratiosfor the hits may also be determined. For example, the program “BCLEAN”,which is a component of the “Figaro” software package developed by KeithShortridge, includes routines that may be used on CCD images to detectand remove bad lines and cosmic ray artifacts from an astronomicalimage. These routines and modifications of it may be used to detectgamma ray artifacts or hits in an image or a stored representation of animage from a CCD or CMOS imager. Rather than removing them from theimage, the routines may be used to identify and characterize gamma raysthat strike the imager.

In an embodiment, a variety of pixel intensity ratios may be calculatedand used to identify extremely sharp-peaked image features or pixelsthat may correspond to gamma rays. These pixels may be flagged andevaluated by other tests.

In an embodiment, every pixel in an image may be evaluated based on aset of user or system constants. For example, C(1), C(2), C(3) and C(4)may be user defined constants (although fewer or more constants are alsopossible). A set of one or more tests to evaluate pixels in an image mayinclude: determining if a pixel data value is greater than zero;determining if a pixel data value is greater than each of the fourclosest pixels (4CP) in the image; determining if a pixel data value isgreater than the average of the 4CP by C(1) counts; determining if apixel data value is greater than the average of the 4CP by C(2) timesthat average; determining if a pixel data value is greater than theaverage of the 4CP by C(3) times the square root of that average; othertests may also be performed. Optionally, a shape parameter may becalculated to assess the general shape of the peak in the image. A ratiomay be constructed of [(the central peak value minus the average of the4CP)/(the average of the 4CP minus the local background average)]. Themethod may determine if this shape ratio is greater than C(4).

Pixels that pass a number of these tests may be considered to beevidence of a gamma ray. For example, a pixel that has passed the firstfive tests, and optionally, the sixth may be considered to be a possiblegamma-ray detection, and in the flow control of FIG. 8, control wouldflow to 816. If no pixels pass all tests, the image is deemed to be freeof gamma rays; the procedure may then consider the next image 804.

If gamma rays are detected in an image 816, the method may be used todetermine how many times gamma rays are detected in the next userdefinable period. The period may be based on a number of frames, whichmay be from 1 to about 1000 frames or 1 to about 15 frames, or an amountof time, which may be from about 0.5 to about 30 seconds, or from about1 to about 10 seconds, although shorter and longer times are possible.If user detected gamma rays are present in the user definable period andthe threshold is exceeded, for example 3-5 frames, the detection may beconsidered to be a persistent, bona fide detection, rather thantransient noise.

The number of gamma rays detected per image may also be used todetermine the veracity of the detection. The user can configure thesystem to ignore frames having fewer than some threshold number ofgamma-ray detections. For example, the threshold may be 1-2 gamma-raydetections per image, but might be set higher in an area with moreambient radiation or at very high altitude. A persistent radioactivesource may trigger an alert and control of the system can flow to 828,but data capture and analysis may continue. All relevant data may belogged and communicated via secure (e.g. encrypted) connection to amonitoring station for further review and possible security operations.

If the activity detected in an image does not repeat, or does not reachthe threshold level, the data may be, optionally, logged, and controlmay be returned to standard data collection acts 804, 808, and 812.

Persistent sources of gamma rays based on pixel or image evaluation maybe interpreted as a radiation event, and trigger defined alerts 824including operator alarm, computer-based alarm, networked alerts,combinations of these and other alerts. In addition to the alerts, anintensive monitoring mode may be activated for the camera that wasresponsible for detecting the radiation event 828. Other cameras, forexample nearby cameras, may be put into a faster data taking andanalysis mode to improve the chances of detecting a radioactive source.If more than one camera detects radiation, those independent detectionsmay be coordinated 832.

Intensive monitoring 828 may have various outcomes includingverification that the radioactive source is still near an approximatelocation, extraction of a more precise location of the radioactivesource, and identification of the specific type of radio-isotope.

Once a positive detection or radioactivity is made, subsequent analysesmay update the current status, without having to revalidate the alertfor persistency. These updates may be used to verify that the source isstill present and may be used for the gradient search in section 828.

Some cameras may be moved by a remote operator, and/or by computercontrol. These cameras may be panned and tilted to alter theirorientation with respect to the radioactive source. As a camera is movedto align its detector more nearly perpendicular to the source, the countrate may increase. Conversely, when the camera is aimed so as to alignthe detector more edge-wise to the radioactive source, the gamma raycount rate may decrease. In this way, a gradient search may be performedeither by the camera operator or by a computer-controlled search (grid,raster, spiral, or other). In one implementation of the gradient search,each time the count rate goes up (averaging over a user-definable numberof frames (for example 3-5 frames), a new gradient search may begin withthe new maximum-count vector defining the search pattern's new origin.When a global maximum is reached, the detector may either be pointingstraight towards, or directly away from the radioactive source. In manycases, the camera's position may make it extremely difficult for asource to be placed in one of these positions (e.g. on the roof of atrain station, or floating in mid-air a short distance above a highway).Images of physical objects detected by the imager may be used to helpdetermine and resolve uncertainties in source location. The digitalcamera data images of physical objects may be used to measure theapparent angular size of identifiable features so as to make estimatesof radioactive source strength. For example, if a car is identified asthe source of activity, the car's distance from the camera imager may bedetermined based upon its apparent angular size and its known length,height, etc. using trigonometric relationships. The calculated distanceand the known sensitivity may be compared to determine if the data areself-consistent.

The energy deposited by the gamma ray in the detector may be measured inaddition to determining the location within the detector and the time ofdetection. The amount of energy deposited into the detector increaseswith increasing gamma ray energy. Every radioisotope may have a uniquespectrum of gamma-ray energies. Measurement of the energy deposited,plus a comparison to a library of energies may permit determination ofthe specific radioisotope. That identity may be reported.

Multiple cameras may detect a specific radioactive source. The data fromeach camera may be analyzed. Each camera may be instructed to carry outan intensive search 828 to identify the specific isotope and to performits own gradient search. By combining the image analysis results fromeach camera, additional information on the source may be obtained.Images from each camera may be used to perform a gradient search. Aseach camera reports a most probable direction from its gradient search,these vectors may be expected to converge towards a single area. Sincethe different cameras are positioned in different locations, theresulting triangulation may facilitate source location determination andmay help in instances where it is not possible for the data from asingle camera to adequately determine a source location. The revisedlocation for the source of radioactivity may be added to the alertinformation.

The coordination of detector data from various imagers may also permit are-determination of radioisotope identity by comparing more data to thelibrary values. A higher significance or confidence in gamma raysidentified in an image may be obtained by combining analysis resultsfrom one or more cameras. The revised estimate of radioactive sourceproperties may be reported via the alert systems.

Example 4

The laboratory experiments performed with small radioactive sourcesconfirm that imagers based on CCD or CMOS platforms are sensitive toenergetic particle impacts. Control experiments verify that theprocedures implemented essentially eliminate false-positive alerts fromoccurring. For such a false alarm to happen, the background rate wouldhave to inexplicably increase by roughly a factor of 20 to 50 and staythat way for seconds. The probability of such an outcome is vanishinglysmall. Similarly, the detections made in the laboratory experimentsresulted in significant detections as shown in FIGS. 6A-6C, even withvery low activity sources. The risk of false-negatives (missed sources)is expected to be small for radioactive sources of a size likely torepresent a viable threat. Radioactive sources that have adisintegration rate of a few thousand Curies, samples large enough topresent a security threat, are expected to be detectable at ranges of atleast a few to several hundred meters, and possibly much further,depending upon the degree of shielding, the air-gap attenuation and theinverse-square fall-off.

The effect of geometric foreshortening reducing the projected solidangle of the detector at angles other than perpendicular to the sourceallow for a gradient search to be executed. This procedure allows formeasurements of activity to be made across a range of pan-tilt (oraltitude-azimuth) orientations. The comparison of measured levels withpointing direction provides a most probable direction vector that pointsalong the line from the current location of the source through thecamera's detector. In many installations, it would be impossible for aradioactive source to be on one of the sides of a camera, reducing thequestion of location to the range along a vector. This outcome wouldoccur, for example, with a camera mounted high on a pole; theradioactive source could not reasonably be expected to be hanging inmid-air nearby. In other instances, shielding on one or more sides ofthe camera may be used to attenuate the gamma rays to differentiateradioactive source location. Alternatively or additionally, data fromnearby cameras may be used to determine the radioactive material sourcelocation.

Example 5

Radon, a decay product of radium-226 emits an alpha particle and mayemit gamma rays (Ra-219) when it decays. Lead, bismuth and thalliumdecay daughter nuclides of Ra-226 can emit gamma rays and may be used todetermine the presence of Radon. For example, the bismuth-214 daughternuclide of Ra-226 emits gamma rays with main energy peaks of 609 keV,1,120 keV, and 1,764 keV gamma rays emitted by the radon decay products.A CCD or CMOS imager may be used to detect Radon and its decay productsin a variety of settings. The imager may be placed in or near an area tobe tested. Optionally, shielding may be used to provide a control. Thedata from the imager may be analyzed for high energy gamma ray particlesto determine the identity and number of counts in the tested area.Alternatively, the capacitor connected to the MOSFET amplifier thatconverts the signal charge to voltage for the imager may be measured forcharge as each pixel is read. A charge or voltage above a giventhreshold may be used to indicate the presence of gamma rays from aradioactive source in the area being tested.

Example 6

In one example of an imager detector, the signal generated by thedetector is the result of gamma rays impinging upon silicon/silicondioxide CCDs. A preliminary study of the gamma ray interaction andenergy deposition into Si/SiO₂ CCD detectors was undertaken and it wasfound that these devices were capable of successfully detectinglead-shielded radioisotopes. Models of two different geometries,representing the extremes likely to be found in realistic fieldoperations were studied. One model involved thin slabs of sourcematerial, minimizing gamma ray self-absorption; the other model was aspherical distribution that maximizes gamma ray self-absorption. Theslab model results supported much higher detection rates, distances andconfidence-levels, but even the spherical models result in detectablesignals at 20-100 meter distances.

Although the present invention has been described in considerable detailwith reference to certain preferred embodiments thereof, other versionsare possible. Therefore, the spirit and scope of the appended claimsshould not be limited to the description and the preferred versionscontained within this specification.

1. A system for detecting high energy particles comprising: at least onelight sensitive pixilated chip comprising pixels configured to produce adigital still image, a digital video image or a combination thereof; atleast one processor in communication with the at least one lightsensitive pixilated chip, said at least one processor being capable ofdetecting one or more pixels that have interacted with at least one highenergy particle and generating an output signal in response to the oneor more pixels that have interacted with at least one high energyparticle in real time; and an output device capable of reporting the atleast one high energy particle.
 2. The system of claim 1, wherein the atleast one pixilated chip is selected from pixilated photon detectorchips, charge coupled devices (CCD), complementary metal oxidesemiconductors (CMOS), and silicon-germanium, germanium,silicon-on-sapphire, indium-gallium-arsenide, cadmium-mercury-telluride,or gallium-arsenide substrate containing chips, and combinationsthereof.
 3. The system of claim 1, wherein the at least one high energyparticle detected by the processor comprises the product of a source ofhigh energy particles wherein the source of high energy particlescomprises a source of nuclear decay of radioactive material.
 4. Thesystem of claim 3, wherein the source of the high energy particle isselected from ambient radiation, radiation from natural sources,radioactive materials, nuclear devices, dirty bombs and nuclear weaponseither before or after detonation, and combinations thereof.
 5. Thesystem of claim 3, wherein the source is shielded.
 6. The system ofclaim 1, wherein a signal is produced when at least one high energyparticle interacts with one or more pixels of the light sensitivepixilated chip.
 7. The system of claim 6, wherein the signal isproportional to the energy of high energy particles that strike thepixel.
 8. The system of claim 6, wherein the signal is stronger thanthat of background radiation.
 9. The system of claim 1, wherein theoutput device displays one or more dots corresponding with each of theone or more high energy particles detected.
 10. The system of claim 1,wherein the at least one processor is capable of identifying a source ofthe at least one high energy particle.
 11. The system of claim 1,wherein the system comprises a plurality of pixilated chips and whereinsaid plurality of pixilated chips are interconnected.
 12. The system ofclaim 1, wherein the at least one pixilated chip is positioned tomonitor objects, wherein said objects are selected from animate andinanimate objects, motor vehicles, airplanes, trains, subway cars,people, animals, buildings, vegetation, luggage, boxes, bags, handbags,briefcases, mail, and combinations thereof.
 13. The system of claim 1,wherein the processor is selected from a computer, a video imageprocessor and combinations thereof.
 14. The system of claim 1, whereinthe output device is selected from an alarm system; a photographic orvideo image; an image on a monitor; an audible sound; a telephone call,a radio transmission and combinations thereof.
 15. The system of claim1, further comprising a processor module configured to determine anumber of pixels that have interacted with the at least one high energyparticle and an energy of the at least one high energy particle, a typeof a source of the at least one high energy particle or an amount of asource of the at least one high energy particle.
 16. The system of claim1, wherein the at least one pixilated chip is completely covered,partially covered or reversibly covered.
 17. A method for detecting highenergy particles comprising: collecting data from one or more lightsensitive pixilated chips comprising pixels for creating a digital stillimage, a digital video image or a combination thereof; identifying fromthe collected data at least one pixel that has interacted with at leastone high energy particle in real time; and detecting a source of the atleast one high energy particle.
 18. The method of claim 17, wherein theone or more light sensitive pixilated chips are selected from the groupconsisting of a charge coupled device (CCD), a complementary metal oxidesemiconductor (CMOS) device, and silicon-germanium, germanium,silicon-on-sapphire, indium-gallium-arsenide, cadmium-mercury-telluride,or gallium-arsenide substrate devices, and combinations thereof.
 19. Themethod of claim 17, wherein the source of the at least one high energyparticle comprises a radioactive material, radioisotope and combinationsthereof.
 20. The method of claim 17, further comprising quantifying achange in charge, voltage, or a combination thereof produced when the atleast one pixel interacts with the at least one high energy particle.21. The method of claim 20, further comprising quantifying an energy forthe at least one high energy particle, a type of the source, an amountof the source, or combinations thereof based on the quantified change incharge.
 22. The method of claim 17, further comprising determining anumber of pixels that have interacted with at least one high energyparticle.
 23. The method of claim 17, further comprising checking forfalse positive detection of a high energy particle.
 24. The method ofclaim 17, further comprising generating an alert when the at least onehigh energy particle is detected.
 25. The method of claim 24, whereinthe alert is selected from the group consisting of an audible alert, avisual alert, and a combination thereof.
 26. The method of claim 17,further comprising tracking the source of the at least one high energyparticle.
 27. The method of claim 26, further comprising continuouslymoving at least one of the one or more light sensitive pixilated chipssuch that at least one high energy particle interacts with at least onepixel of the at least one continuously moving light sensitive pixilatedchip.
 28. The method of claim 26, further comprising identifying aposition where at least one pixel of the at least one continuouslymoving light sensitive pixilated chips has a maximum probability ofinteracting with at least one high energy particle.
 29. The method ofclaim 26, further comprising adjusting the at least one continuouslymoving light sensitive pixilated chips until the light sensitivepixilated chip is perpendicular to the source of the at least one highenergy particle.
 30. The method of claim 26, further comprising:coordinating at least a first light sensitive pixilated chip and atleast a second light sensitive pixilated chip; moving each of the atleast first and second light sensitive pixilated chips independently;identifying a position where at least one pixel of the first lightsensitive pixilated chip has a maximum probability of interacting withat least one high energy particle; identifying a position where at leastone pixel of the second light sensitive pixilated chip has a maximumprobability of interacting with at least one high energy particle;triangulating a position of a source of the at least one high energyparticle using the identified positions of each of first and secondlight sensitive pixilated chips.
 31. The method of claim 17, furthercomprising determining a brightness of the at least one pixel.
 32. Themethod of claim 31, further comprising determining at least one of: anumber of pixels that have interacted with the at least one high energyparticle; an energy of the at least one high energy particle; a type ofthe source; or an amount of the source based on the brightness of the atleast one pixel.
 33. The method of claim 32, wherein the one or morelight sensitive pixilated chips are completely covered, partiallycovered or reversibly covered.